Controlling apparatus and method

ABSTRACT

This invention resides in a method and apparatus for controlling the flow of first and second fluid streams together to form a composite stream having a preselected composition range. Said composition range is maintained by the controlling apparatus and method during fluctuation of the supply of one or both of said fluid streams.

United States Patent Remke ]March 20, 1973 CONTROLLING APPARATUS AND3,090,683 5/1963 Berger ..48/196 R METHOD 3,206,394 9/1965 Kleiss et a1...48/l96 R x 3,250,757 5/1966 Smith et al ..23/253 A [75] RemkeBartlesvlue 3,254,071 5/1966 Morgan et a1. ..23/253 A Okla- 3,298,3831/1967 Cooper ..137/3 [73] Assignee: Philips Petroleum Company,3,322,136 5/1967 Matta ..137/118 Bartlesvme, Okla 3,419,369 12/1968Kelley ..4s 196 R [22] Filed: Sept. 24, 1971 Primary Examiner-Martin P.Schwadron [21] Appl' No: 183,473 Assistant Examiner-David J. Zobkiw IAtt0rneyYoung & Quigg [52] US. Cl. ..l37/3, 23/230 A, 23/253 A, 57ABSTRACT 48/190,48/196, 137/7, 137/88,137/90 1 [51] Int. Cl. ..G05d11/02 This n nti n s d in a m th d and apparatus for [58] Field ofSearch,, 23/23O A, 253 A; 48/190, 196; controlling the flow of first andsecond fluid streams 137/2, 3, 7, 12, 88, 90 together to form acomposite stream having a preselected composition range. Saidcomposition [56] References Cited range is maintained by the controllingapparatus and method during fluctuation of the supply of one or bothUNITED STATES PATENTS of Said fluid Streams.

2,072,384 3/1937 Schmidt ..137/90 X 2,436,041 2/1948 Gerhold et a1196/132 x 10 Claims, 1 Drawing "8"" 2,702,238 2/1955 Hays ..48/l96 RCONTROLLING APPARATUS AND METHOD it is often desirable to provideapparatus and method for controlling the flow rates of first and secondfluid streams for providing a composite stream having preselectedproperties. An example of where such control is desirable is in theblending of air with a hydrocarbon fuel gas to lower the calorific valueof the resulting blend and maintain said calorific value in apreselected range during fluctuations in the supply of one or both ofthe gases. It should be understood, however, that the apparatus andmethod of this invention can be used in controlling the blending of manymaterials in a wide variety of applications for providing a compositestream having certain preselected properties.

Other aspects, objects, and advantages of the present invention willbecome apparent from a study of the disclosure, the appended claims, andthe drawing.

The drawing is a diagrammatic view of the first stream, the secondstream, the composite stream, and the-controlling equipment associatedtherewith.

Referring to the drawing, first and second fluid streams 2, 4 are joinedone with the other to form a composite stream 6. A first flow measuringelement 8 and a second flow measuring element 10, such as for exampleconventional orifice meter runs, are associated with their respectivefirst and second fluid streams 2,4 for measuring the flow rates of thestreams. The first flow measuring element 8 delivers a signal Arepresentative of the measured flow rate of the first stream 2 and thesecond flow measuring element 10 delivers a signal B representative ofthe measured flow rate of the second stream 4.

It is preferred in this invention that the signals delivered by thevariousapparatus described herein be pneumatic signals for providing acontrolling system that is easy to install and maintain, is of quickresponse andprovides safety with simple construction. The controls canhowever be electrical, electronic or other types. It is also preferredthat the various functions of the apparatus be performed continuously byanalog apparatus, but it is within the scope of this invention that saidfunctions such as measurements, signal deliveries, signal comparisons,analyses, etc., or a portion thereof can be conducted intermittently,such as by direct digital control, as opposed to continuously.

An analyzing element 12 is associated with the composite stream 6 formeasuring at least one constituent of said composite stream anddelivering a signal C representative of the concentration of saidconstituent. The type of analyzer utilized is dependent upon the type offirst and second streams desired to be mixed one with the other to formthe composite stream and the property of the composite stream that isdesired to be maintained within the preselected range. Where the firststream 2 is a hydrocarbon fuel gas and the second stream 4 is air andthe calorific value of the composite stream is desired to be maintainedwithin a preselected range, for example, it is then preferred that theanalyzer 12 be a paramagnetic oxygen analyzer such as manufactured byHays Corporation, Michigan City, Indiana, adapted to deliver a signalrepresentative of the concentration of oxygen contained in the compositestream 6. One skilled in the art after studying the construction andmethod of the invention can determine the particular analyzer and signalfor the constituent he desires to control.

A controller 14 having a set point D is available from manymanufacturers such as The Foxboro Co., Foxboro, Massachusetts and SybronCorporation, Taylor Instrument Process Control Division, Rochester, NewYork, and is connected to the analyzing element 12 for receiving thesignal C therefrom, comparing said signal C to its set point D anddelivering a signal E responsive to the difference between the set pointD and the signal C.

A first process control valve 16 is provided in the .first stream 2 forregulating the flow rate of the first stream 2 in response to ahereinafter-described signal J. A second control valve 18 is positionedin the second stream 4 for regulating the flow rate of the second stream4 in response to a hereinafter-described signal L.

A pressure control means 20 having a set point M, such as iscommercially available, is associated with the first stream 2 at alocation upstream of the first control valve 16 for measuring the supplypressure of the first stream .2, comparing said measurement to its setpoint M, and delivering a signal F responsive to the difference betweenthe set point value and the pressure measurement of the first stream 2.

A first ratio relay 22 having a set point N is connected to the firstflow measuring element 8 for receiving the signal A therefrom,multiplying said signal A by its set point N, and delivering a signal Grepresentative of said product of multiplication. A second ratio relay24 having a set point P is connected to the second flow measuring.element 10 for receiving the signal B therefrom, dividing said signal Bby its set point P, and delivering a signal H representative of saidquotient of division. The first ratio 'relay 22 can be, for example,Foxboro Series 556-8-80 Ratio Computing Relay available from The FoxboroCo., Foxboro, Massachusetts. The second ratio relay 24 can be, forexample, Foxboro Series 556-9-80 Ratio Computing Relay.

It should also be understood that in the specific example of thiscontrolled blending process, the division or multiplication performed bythese ratio relays 24,22 can utilize set points P and N calibrated interms of airto-gas ratio or percent air (or oxygen) as desired inblended stream 6. The signal G delivered from the first ratio relay 22is therefore responsive to the requirements of the first stream 2, andthe signal H delivered from the second ratio relay 24 is thereforeresponsive to the requirements of the second stream 4.

The first selective relay 26 is connected to the first ratio relay 22and the controller 14 for receiving signals G and E therefrom, comparingsaid signals G and E one to the other, and delivering a signal Irepresentative of the lower one of said signals G and E.

A first flow controller 30 is connected to the second ratio relay 24 andthe first flow measuring element 8 for receiving signals H and Atherefrom, comparing signals H and A one to the other, and delivering asignal K responsive to the difference between signals H and A to thesecond selective relay 28. The second selective relay 28 is connected tothe first flow controller 30, and to the pressure controller 20, forreceiving signals K and F, comparing signals K and F one to the other,and, in response to the comparison, delivering the higher of saidsignals as signal J to the valve for controlling the flow rate of thefirst stream 2 relative to one of the flow rate of the second fluidstream 4 or the supply pressure of said first stream 2. A second flowcontroller 32 is connected to the first selective relay 26 and thesecond flow measuring element for receiving signals 1 and B therefrom,comparing I and B one to the other, and delivering a signal L responsiveto the difference between signals I and B to the second control valve 18for controlling the flow rate of the second fluid stream 4 relative toone of the flow rate of the first stream 2 or the analysis of thecomposite stream 6.

The first and second flow controllers 30, 32 are available from manymanufacturers, such as The Foxboro Co., Foxboro, Massachusetts, andSybron Corporation,- Taylor Instrument Process Control Division,Rochester, New York. Control valves 16,18 are likewise available frommany manufacturers and in the specific example described are desirablyof the normally closed (pneumatic pressure opens) type. The selectiverelays 26, 28 can be respectively, for example, Moore Products SelectiveRelays Model 61F for low signal pressure selection and Model 588 forhigh signal pressure selection. Both are made by Moore Products Company,Spring House, Pa.

A conduit loop 34 is provided with said loop being in communication withthe first fluid stream 2 on opposed sides of the first control valve 16and with said loop 34 having a compressor 36 therein for increasing thepressure of said first fluid stream 2. In order to obtain a moreaccurate measurement of the flow rates of the first and second streams2, 4, it is preferred that the first flow measuring element 8 be locateddownstream of the first control valve 16 and downstream of saidcompressor 36, and the second flow measuring element 10 is locateddownstream of the second control valve 18. Further, in the preferredembodiment of this apparatus, particularly where the first fluid stream2 is a hydrocarbon gas and the second fluid stream 4 is a fluid utilizedfor lowering the calorific value of the gas, it is preferred that theset points of the first and second ratio relay 22, 24 are valuessufficient for maintaining the composite stream within a preselectedcalorific value, for example in the range of about 970 to about 1040Btu/standard cubic foot at 60 F. and 14.65 psia.

In the method of this invention in addition to that described above withrespect to each element of the apparatus, after the operator hasselected the first and second fluids and the constituent of the secondstream desired as a representative constituent for controlling thecomposite stream, the various corresponding set points D, M, N, P areselected for the control system. The second flow controller 32 and itsassociated signals thereto provide for controlling the second streamflow rate at a maximum value for producing the composite stream with amaximum concentration of said second stream during periods when thefirst fluid stream 2 is in limited supply, and the first flow controllerby way of second selective ratio relay 28 maintains the first streamflow rate at a maximum value for producing the composite stream with theminimum concentration of said second stream during periods when thesecond fluid stream 4 is in limited supply.

The control signal E from controller 14 by way of selective relay 26 canbe utilized for limiting the flow rate of the second stream when theanalysis indicates that a preselected high oxygen concentration of thecomposite stream has been reached.

By controlling the mixing of the first and second streams 2, 4 by themethod and apparatus of this invention, the composite stream isautomatically maintained within a preselected composition range, in aspecific example between 11 to 15 percent air in natural gas, duringperiods when one or both of the first and second flow streams flow ratesare fluctuating due to supplydemand relationships. The resultantcomposite stream is therefore of a more uniform and safe composition andbetter suited for the purpose for which said composite stream isutilized. A conventional mixer 38 may be inserted at the junction offirst stream 2 and second stream 4 to insure thorough mixing of saidstreams.

Other modifications and alternations of this invention will becomeapparent to those skilled in the art from the foregoing discussion andaccompanying drawing, and it should be understood that this invention isnot to be unduly limited thereto.

What is claimed is:

1. An apparatus for separately regulating the flow rates of first andsecond fluid streams joining one with the other to form a compositestream for maintaining said composite stream within a preselectedcomposition range, comprising:

first flow measuring means for measuring the flow rate of the firststream and delivering a signal A representative of that flow rate;

second flow measuring means for measuring the flow rate of the secondstream and delivering a signal B representative of that flow rate;

an analyzing means associated with the composite stream for measuring atleast one constituent of said composite stream and delivering a signal Crepresentative of the relative amount of said constituent;

a control means having a set point D and being connected to theanalyzing means for receiving the signal C therefrom, comparing saidsignal C to the set point D and delivering a signal E responsive to thedifference between the set point D and the signal C;

a first control valve positioned in the first stream for regulating theflow rate of the first stream in response to a received signal;

a conduit loop in communication with the first stream on' opposed sidesof the first control valve;

a compressor positioned in the conduit loop;

a second control valve positioned in the second stream for regulatingthe flow rate of the second stream in response to a received signal;

a pressure control means associated with the first stream at a locationupstream of the first control valve for measuring the pressure of saidfirst stream, comparing said measurement to a set point, and deliveringa signal P responsive to the difference between the set point value andthe pressure measurement of the first stream;

a first ratio relay means having a set point and being connnected to thefirst flow measuring means for receiving the signal A therefrom,multiplying said signal A by the set point, and delivering a signal Grepresentative of said multiplication;

a second ratio relay means having a set point and being connected to thesecond flow measuring means for receiving the signal B therefrom,dividing said signal B by the set point and delivering a signal Hrepresentative of said division;

a first selective relay means connected to the first ratio relay meansand the control means for receiving E and G, comparing said signals Eand G one to the other, and delivering a signal I representative of thelower of said signals E and G;

a first flow controller connected to the second ratio relay and thefirst flow measuring means for receiving signals A and H, comparingsignals A and H one to the other and delivering a signal K responsive tothe difference between signals A and a second selective relay meansconnected to the first flow controller, the first valve and the pressurecontrol means for receiving signals F and K, comparing said signals Fand K one to the other, and delivering s signal J representative of thehigher of said signals F and H to the first valve for controlling theflow rate of the first stream relative to one of the flow rate of thesecond stream or the pressure of the first stream; and

a second flow controller connected to the first selective relay, thesecond flow measuring means, and the second valve for receiving signalsB and l, comparing signals B and lone to the other, and delivering asignal L responsive to the difference between signals B and l to thesecond valve for controlling the flow rate of the second stream relativeto one of the flow rate of the first stream or the analysis of thecomposite stream.

2. An apparatus, as set forth in claim 1, wherein the analyzing means isa paramagnetic oxygen analyzer.

3. An apparatus, as set forth in claim'l, wherein the set point of thefirst ratio relay means is a value representative to the desired flowrate of the second stream divided by the desired flow rate of the firststream and the set point of the second ratio relay means is a valuerepresentative to the desired flow rate of the second stream divided bythe desired flow rate of the first stream.

4. An apparatus, as set forth in claim 1, wherein the first flowmeasuring means is located downstream of the first control valve and thesecond flow measuring means is located upstream of the second controlvalve.

5. An apparatus, as set forth in claim 1, wherein the signals arepneumatic signals.

6. An apparatus, as set forth in claim 1, wherein the first fluid streamis a gaseous hydrocarbon stream and the second fluid stream is air.

7. An apparatus, as set forth in claim 6 wherein the set points of thefirst and second ratio relay means are values for maintaining thecomposite stream within a preselected calorific range.

8. An apparatus, as set forth in claim 1, wherein the analyzing meansmeasures the oxygen content of the composite stream and the second fluidstream comprises air.

9. A method for regulating the How rates of first and second fluidstreams joining one with the other to form the composite stream formaintaining said composite stream within a preselected compositionrange, comprising:

measuring the flow rate of the first stream;

delivering a signal A representative of the flow rate of said firststream;

measuring the flow rate of the second stream;

delivering a signal B representative of the flow rate of said secondstream; measuring at least one constituent of said composite stream;

delivering a signal C representative of the relative amount of saidmeasuring constituent;

comparing signal C to a set point D;

delivering a signal E responsive to the difference between the set pointD and the signal C;

measuring the pressure ofsaid first stream;

delivering a signal F responsive to the difference between a set pointvalue and the pressure measurement of the first stream;

multiplying signal A by a set point value;

delivering a signal G representative of said multiplication;

dividing signal B by a set point value;

delivering a signal H representative of the quotient of a division ofsignal B by an associated set point value;

comparing the signals E and G one to the other;

delivering a signal I representative of the lower of said signals E andG;

comparing signals A and H one to the other;

delivering a signal K responsive to the difference between signals A andH;

comparing signals Fand K one to the other;

delivering a signal J in response to the comparison;

receiving signal J and controlling the flow rate of the first stream inresponse to said signal J;

comparing signals B and lone to the other;

delivering a signal L responsive to the difference between signals B and1;

receiving signal L and controlling the flow rate of the second stream inresponse to said signal L.

10. A method, as set forth in claim 9, wherein the constituent measuredis oxygen.

1. An apparatus for separately regulating the flow rates of first andsecond fluid streams joining one with the other to form a compositestream for maintaining said composite stream within a preselectedcomposition range, comprising: first flow measuring means for measuringthe flow rate of the first stream and delivering a signal Arepresentative of that flow rate; second flow measuring means formeasuring the flow rate of the second stream and delivering a signal Brepresentative of that flow rate; an analyzing means associated with thecomposite stream for measuring at least one constituent of saidcomposite stream and delivering a signal C representative of therelative amount of said constituent; a control means having a set pointD and being connected to the analyzing means for receiving the signal Ctherefrom, comparing said signal C to the set point D and delivering asignal E responsive to the difference between the set point D and thesignal C; a first control valve positioned in the first stream forregulating the flow rate of the first stream in response to a receivedsignal; a conduit loop in communication with the first stream on opposedsides of the first control valve; a compressor positioned in the conduitloop; a second control valve positioned in the second stream forregulating the flow rate of the second stream in response to a receivedsignal; a pressure control means associated with the first stream at alocation upstream of the first control valve for measuring the pressureof said first stream, comparing said measurement to a set point, anddelivering a signal F responsive to the difference between the set pointvalue and the pressure measurement of the first stream; a first ratiorelay means having a set point and being connnected to the first flowmeasuring means for receiving the signal A therefrom, multiplying saidsignal A by the set point, and delivering a signal G representative ofsaid multiplication; a second ratio relay means having a set point andbeing connected to the second flow measuring means for receiving thesignal B therefrom, dividing said signal B by the set point anddelivering a signal H representative of said division; a first selectiverelay means connected to the first ratio relay means and the controlmeans for receiving E and G, comparing said signals E and G one to theother, and delivering a signal I representative of the lower of saidsignals E and G; a first flow controller connected to the second ratiorelay and the first flow measuring means for receiving signals A and H,comparing signals A and H one to the other and delivering a signal Kresponsive to the difference between signals A and H; a second selectiverelay means connected to the first flow controller, the first valve andthe pressure control means for receiving signals F and K, comparing saidsignals F and K one to the other, and delivering s signal Jrepresentative of the higher of said signals F and H to the first valvefor controlling the flow rate of the first stream relative to one of theflow rate of the second stream or the pressure of the first stream; anda second flow controller connected to the first selective relay, thesecond flow measuring means, and the second valve for receiving signalsB and I, comparing signals B and I one to the other, and delivering asignal L responsive to the difference between signals B and I to thesecond valve for controlling the flow rate of the second stream relativeto one of the flow rate of the first stream or the analysis of thecomposite stream.
 2. An apparatus, as set forth in claim 1, wherein theanalyzing means is a paramagnetic oxygen analyzer.
 3. An apparatus, asset forth in claim 1, wherein the set point of the first ratio relaymeans is a value representative to the desired flow rate of the secondstream divided by the desired flow rate of the first stream and the setpoint of the second ratio relay means is a value representative to thedesired flow rate of the second stream divided by the desired flow rateof the first stream.
 4. An apparatus, as set forth in claim 1, whereinthe first flow measuring means is located downstream of the firstcontrol valve and the second flow measuring means is located upstream ofthe second control valve.
 5. An apparatus, as set forth in claim 1,wherein the signals are pneumatic signals.
 6. An apparatus, as set forthin claim 1, wherein the first fluid stream is a gaseous hydrocarbonstream and the second fluid stream is air.
 7. An apparatus, as set forthin claim 6 wherein the set points of the first and second ratio relaymeans are values for maintaining the composite stream within apreselected calorific range.
 8. An apparatus, as set forth in claim 1,wherein the analyzing means measures the oxygen content of the compositestream and the second fluid stream comprises air.
 9. A method forregulating the flow rates of first and second fluid streams joining onewith the other to form the composite stream for maintaining saidcomposite stream within a preselected composition range, comprising:measuring the flow rate of the first stream; delivering a signal Arepresentative of the flow rate of said first stream; measuring the flowrate of the second stream; delivering a signal B representative of theflow rate of said second stream; measuring at least one constituent ofsaid composite stream; delivering a signal C representative of therelative amount of said measuring constituent; comparing signal C to aset point D; delivering a signal E responsive to the difference betweenthe set point D and the signal C; measuring the pressure of said firststream; delivering a signal F responsive to the difference between a setpoint value and the pressure measurement of the first stream;multiplying signal A by a set point value; delivering a signal Grepresentative of said multiplication; dividing signal B by a set pointvalue; delivering a signal H representative of the quotient of adivision of signal B by an associated set point value; comparing thesignals E and G one to the other; delivering a signal I representativeof the lower of said signals E and G; comparing signals A and H one tothe other; delivering a signal K responsive to the difference betweensignals A and H; comparing signals F and K one to the other; deliveringa signal J in response to the comparison; receiving signal J andcontrolling the flow rate of the first stream in response to said signalJ; comparing signals B and I one to the other; delivering a signal Lresponsive to the difference between signals B and I; receiving signal Land controlling the flow rate of the second stream in response to saidsignal L.
 10. A method, as set forth in claim 9, wherein the constituentmeasured is oxygen.